Patterning of microscale and nanoscale structures in three dimensions can be difficult for a variety of reasons. In the conventional sense, such patterning is achieved by performing a layer-by-layer patterning of 2D (two dimensional) planes. This can be tedious, time consuming and expensive. Challenges may also exist for aligning one layer on top of another.
Another approach to 3D (three dimensional) patterning is via the use of two-photon lithography. In this approach, a laser beam is focused into a small diffraction-limited spot inside a photosensitive material. This material is designed so as to undergo a two-photon reaction. Typically, this reaction results in polymerization. Since the two-photon reaction is sensitive to the intensity of light, the reaction only occurs substantially in a narrow 3D region at the center of the focal spot.
Conventional lithography is performed on flat (planar) surfaces and materials and layers are built up via multiple patterned layers each formed by deposition of a layer followed by substractive processing. Therefore, patterning non-planar surfaces using such approaches presents additional challenges and is generally more difficult or impossible depending on surface geometry and desired patterns.